1. Field of the Invention
This invention is directed to methods for reclaiming abandoned settling ponds utilized in strip mining operations by draining water from the ponds while stabilizing such areas by drying clay pumped from subsurface levels and, more particularly, to a method of reclamation wherein lightweight amphibious vehicles are utilized to traverse low level areas. The method utilizes high pressure pumps which withdraw clay from below the surface of the ponds and to distribute the clay remotely on adjacent stabilized or crusted surface areas so that drying of the clay by evaporation and exposure to the sun is promoted. The withdrawal of the clay causes adjacent surface areas to fall creating stabilized ditches of gentle profile which are used to drain water to the perimeter areas of the ponds thereby allowing a relative continuous drainage of water from the ponds while simultaneously facilitating the drying of clay withdrawn therefrom.
Utilizing the methodology of the present invention, low level areas within the ponds may be connected by stabilized drainage ditches or channels to naturally occurring streams, which are also stabilized by removing clay therefrom. The streams extend to the perimeters of the ponds thereby creating a network of drainage ditches which follow natural surface contours thus facilitating the removal of water from the ponds.
2. History of the Related Art
In the strip mining of phosphate and other resources, the phosphate ore is conventionally mixed with water and pumped to processing plants where the ore is washed and graded before being further processed to remove the phosphate from the soil. During the processing, the water which is utilized to convey the phosphate ore is discharged as a watery clay mixture into large settling ponds wherein the water is allowed to slowly seep into the soil. The settling ponds are generally constructed by initially forming earthen dams or dikes around the perimeter of an area. Many times the bottom will have an uneven contour remaining after mining operations. Such dikes often extend as high as fifty feet. Vast acres of land are bordered by such dikes to create settling ponds capable of handling multiple millions of gallons of water and discharged clay per day. To conserve on resources, the clear water from the top of the settling ponds is normally drained off and recycled and used in the conveying and processing of the phosphate ore, however, in some instances, the water may be discharged to adjacent waterways. As the ponds fill with clay, they are abandoned in favor of newly formed settling ponds. After the ponds are closed or abandoned, they must be reclaimed by draining remaining surface waters and allowing the settled clay to dry so that the earth may be reworked to allow its natural use. As the clay dries a crust of dehydrated clay will form on the surface. The underlying clay has a pudding-like consistency and contains of approximately 20% dry solids by weight.
Conventional methods of settling pond reclamation rely on the formation of ditches which extend inwardly from a perimeter ditch dug adjacent to the dike inner wall. These ditches form conveyance channels for drainage of water from the settling ponds. Unfortunately, the degree of ditch formation is severely limited as the surface areas within the ponds are not stable and do not provide sufficient support or bearing capacity for most earthworking equipment. Therefore, ditching is limited to only those perimeter areas wherein conventional backhoes and other types of ditching equipment can be supported on stabilized soil. A further problem with conventional methods is that after ditches have been formed, as water is being drained through the ditches, the underlying clay layer starts to shrink as it dehydrates. This shrinkage causes the surface level to fall as the crust is no longer being supported by the underlying clay.
Parts of the ditches in these areas drop with the surface areas to the extent that the ditch bottom, which was originally sloped toward the perimeter for drainage, now slopes toward the center of the pond and must be reexcavated. In order to maintain the drainage slope toward the perimeter, the ditches must be made deeper as they approach the perimeter. The material removed is deposited on the surface adjacent to the deepened ditch. This additional weight on the crust coupled with the greater depth causes clay to flow from the subsurface areas into the ditch and the ditch walls to collapse, thereby interrupting the drainage of water and inhibiting the reclamation process.